Seal Ring for Hybrid-Bond

ABSTRACT

A structure includes a first die and a second die. The first die includes a first bonding layer having a first plurality of bond pads disposed therein and a first seal ring disposed in the first bonding layer. The first bonding layer extends over the first seal ring. The second die includes a second bonding layer having a second plurality of bond pads disposed therein. The first plurality of bond pads is bonded to the second plurality of bond pads. The first bonding layer is bonded to the second bonding layer. An area interposed between the first seal ring and the second bonding layer is free of bond pads.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/429,735, filed on Jun. 3, 2019, entitled “Seal Ring for Hybrid-Bond”,which is a continuation of U.S. patent application Ser. No. 16/003,654,filed Jun. 8, 2018, entitled “Seal Ring for Hybrid-Bond”, (now U.S. Pat.No. 10,312,201, issued Jun. 4, 2019), which claims priority to and thebenefit of U.S. Provisional Application No. 62/592,856, filed on Nov.30, 2017, entitled “Seal Ring for Hybrid-Bond,” which application ishereby incorporated herein by reference in its entirety.

BACKGROUND

In wafer-to-wafer bonding technology, various methods have beendeveloped to bond two package components (such as wafers) together. Theavailable bonding methods include fusion bonding, eutectic bonding,direct metal bonding, hybrid bonding, and the like. In the fusionbonding, an oxide surface of a wafer is bonded to an oxide surface or asilicon surface of another wafer. In the eutectic bonding, two eutecticmaterials are placed together, and are applied with a high pressure anda high temperature. The eutectic materials are hence molten. When themelted eutectic materials are solidified, the wafers are bondedtogether. In the direct metal-to-metal bonding, two metal pads arepressed against each other at an elevated temperature, and theinter-diffusion of the metal pads causes the bonding of the metal pads.In the hybrid bonding, the metal pads of two wafers are bonded to eachother through direct metal-to-metal bonding, and an oxide surface of oneof the two wafers is bonded to an oxide surface or a silicon surface ofthe other wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a schematic top view of wafer, in accordance withsome embodiments.

FIGS. 2a through 2c illustrate various views of a die, in accordancewith some embodiments.

FIG. 3 illustrates a schematic top view of wafer, in accordance withsome embodiments.

FIGS. 4a through 4c illustrate various views of a die, in accordancewith some embodiments.

FIG. 5 illustrates a cross-sectional view of two bonded dies, inaccordance with some embodiments.

FIG. 6 illustrates a schematic top view of wafer, in accordance withsome embodiments.

FIGS. 7a through 7c illustrate various views of a die, in accordancewith some embodiments.

FIG. 8 illustrates a schematic top view of wafer, in accordance withsome embodiments.

FIGS. 9a through 9c illustrate various views of a die, in accordancewith some embodiments.

FIGS. 10a through 10c and FIG. 11 illustrates various views of twobonded dies, in accordance with some embodiments.

FIG. 12 illustrates a schematic top view of wafer, in accordance withsome embodiments.

FIGS. 13a through 13c illustrate various views of a die, in accordancewith some embodiments.

FIG. 14 illustrates a cross-sectional view of two bonded dies, inaccordance with some embodiments.

FIG. 15 illustrates a cross-sectional view of two bonded dies, inaccordance with some embodiments.

FIG. 16 illustrates a cross-sectional view of two bonded dies, inaccordance with some embodiments.

FIG. 17 is a flow diagram for altering the design layout of bond pads ona die, in accordance with some embodiments.

FIG. 18 is a flow diagram for altering the design layout of bond pads ona die, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments described herein provide a hybrid bonding of two distinctdies. Dies may be designed with bond pads to provide electrical andmechanical attachment points to bond another die or device thereto toform a package. Some of these bond pads may be “active,” that is,electrically coupled to a component within the die, or “dummy,” that is,electrically decoupled (e.g., floating) from any component with in thedie. When a die is hybrid bonded to another die or component, dielectricmaterials at the surface of each die are aligned and fusion bondedtogether and metal bond pads in each die are aligned and directly bondedtogether. Die formation and processing to achieve suitable matingsurfaces for hybrid bonding have heightened tolerances to help achieve astronger or more reliable bonding. As such, to avoid tolerance variancesresulting from die processing, such as dishing, a bond pad pattern isusually carried out over the entire surface of the die so that ChemicalMechanical Polishing (CMP) processes or the like uniformly affect thesurface of the die for a predictable and uniform result. In someembodiments of the present disclosure, however, the design of the diesis altered to provide a zone where dummy bond pads are removed formating to an area over a seal ring structure. Removing the dummy bondpads from the layout has been shown to increase bonding yield,especially where the spacing of the bond pads in the pattern is small.In other embodiments, rather than removing the dummy bond pads, thedesign is altered to mechanically and electrically couple the dummy bondpads to the seal ring. Embodiments described herein may be used indie-on-die, wafer-on-wafer (WoW), chip-on-chip (CoC), or chip-on-wafer(CoW) hybrid bonding processes where dummy bond pads are removed from anotherwise uniform contact pad layout design on the die, dummy bond padsare coupled to a seal ring, or a combination thereof.

Referring to the illustrated drawings, in Figures providing multipleviews, Figures ending in an “a” indicate a perspective viewillustration, figures ending in a “b” indicate a cross-section viewillustration, and figures ending in a “c” indicate a top down view orplan view illustration. FIGS. 1-5 illustrate intermediate stages of ahybrid bonding technique, in accordance with some embodiments. FIGS. 1through 2 c illustrate a die 112, FIGS. 3 through 4 c illustrate anotherdie 212, and FIG. 5 illustrates a hybrid bonding of die 112 with die212, in accordance with some embodiments.

FIG. 1 illustrates a schematic top view of wafer 100 in accordance withsome embodiments. Wafer 100 includes dies 112 and the adjoining scribelines 114 and scribe lines 116, wherein scribe lines 114 and scribelines 116 separate dies 112 from each other. Scribe lines 114 havelongitudinal directions parallel to the X direction, and scribe lines116 have longitudinal directions parallel to the Y direction, which isperpendicular to the X direction. In each of dies 112, there may be oneor more seal rings (e.g., shown as 136 in FIG. 2a ), wherein the outerboundaries of the seal ring unit 136 define the outer boundaries of dies112. Each of the scribe lines 114 is between and adjoining two rows ofdies 112, and each of the scribe lines 116 is between and adjoining twocolumns of dies 112. It is noted that wafer 100 is intended to be anexample only, and the sizes of dies 112, scribe lines 114 and scribelines 116, etc. may vary based on the die designs.

FIG. 2a illustrates a schematic perspective view of die 112. Die 112 inFIG. 2a may be singulated from wafer 100 or may still be intact withwafer 100. Seal ring unit 136 (shown in phantom) is disposed at aperiphery of die 112 under the surface of the die and may include one ormore distinct seal rings (described in greater detail below with respectto FIGS. 2b and 2c ). In some embodiments, die 112 comprises an array ofbond pads 142 set over and around a device area 118 of die 112. In someembodiments, the device area 118 may include the entire area of die 112within seal ring unit 136. In other embodiments, the device area 118 mayinclude a portion of the area of die 112 within seal ring unit 136, suchas illustrated in FIG. 2a . In some embodiments, the device area 118 mayinclude all the available bond pads 142 on the die or a subset of theavailable bond pads 142. Arrangements of bond pads 142 may be made in apattern other than an array pattern. Bond pads 142 may be sizedsimilarly or differently, depending on the design of the bond pads 142on die 112.

Die 112 may include a logic device, micro-electro-mechanical systems(MEMS) device, integrated passive device (IPD), driver, or memory devicesuch as memory cells including, and not limited to, Static Random AccessMemory (SRAM) cells, Dynamic Random Access Memory (DRAM) Cells,Magneto-Resistive Random Access Memory (MRAM) cells, or the like. Die112 may include other types of devices.

Die 112 may have first width, e.g., in the X direction of w1, which maybe between about 2000 μm and about 26000 μm, such as about 10000 μm. Die112 may have second width (or length), e.g., in the Y direction of w2,which may be between about 2000 μm and about 33000 μm, such as about10000 μm. Other dimensions for die 112 may be used.

FIG. 2b illustrates a cross-sectional view of die 112. The cross-sectionof FIG. 2b is a portion of a cross-section taken along the line A-A ofFIG. 2c , however the details may be varied from one view to another forthe purposes of discussion. Die 112 includes a substrate 122, which maybe a semiconductor substrate, such as a silicon substrate, a silicongermanium substrate, a silicon carbon substrate, an III-V compoundsemiconductor substrate, or the like. A device area 118 is formed at thesurface or inside substrate 122. Device area 118 may comprise active orpassive devices, such as transistors, resistors, capacitors, diodes, andthe like. In some embodiments, device area 118 may comprise anencapsulated die.

An interconnect structure 126 may be formed over the substrate 122.Interconnect structure 126 may include insulating layers 128, such as aninter-layer dielectric (ILD) and/or inter-metal dielectric layers (IMD)and conductive features (e.g., metal lines 127 and vias 129) formed inalternating layers over substrate 122 using any suitable method.Interconnect structure 126 may connect various active and/or passivedevices in device area 118 of substrate 122 to form functional circuits.The insulating layers 128 may comprise low-k dielectric materials havingk values, for example, lower than about 4.0 or even 2.8. In someembodiments, insulating layers 128 may comprise undoped silicate glass(USG), spin-on carbon, and the like. The thickness t1 of interconnectstructure 126 may be between about 0.1 μm and about 6 μm, such as about4 μm. Other thicknesses may be used.

In some embodiments where device area 118 is an area of substrate 122used to create various active and passive devices, interconnectstructure 126 may be formed using a dual damascene process. A dualdamascene process may include, for example, depositing insulating layers128 (which may be formed as single layers or multiple layers separatedby one or more etch stop layers), forming trenches in and via openingsin the insulating layers to expose some portions of the metal lines 127and vias 129, and filling the trenches and via openings with aconductive material to form more metal lines 127 and vias 129. Optionalmetal pads 131 can be formed in a top most layer of the interconnectstructure 126 in a manner similar to forming the metal lines 127. A CMPis then performed to remove excess conductive material. Accordingly, theportions of the conductive material filling the trenches in theinsulating layers 128 become the metal lines 127, respectively, whilethe portions of the conductive material filling the via openings becomevias 129.

In embodiments where device area 118 is an encapsulated die, in anexample to form interconnect structure 126, first an insulating layer128 may be deposited over the substrate 122 and device area 118. In someembodiments, the insulating layer 128 is formed of a polymer, which maybe a photo-sensitive material such as PBO, polyimide, BCB, or the like,that may be patterned using a lithography mask. In other embodiments,the insulating layer 128 is formed of a nitride such as silicon nitride;an oxide such as silicon oxide, PSG, BSG, BPSG; or the like. Theinsulating layer 128 may be formed by spin coating, lamination, CVD, thelike, or a combination thereof. The insulating layer 128 may be formedof low-k materials.

The insulating layer 128 is then patterned. The patterning formsopenings to expose portions of substrate 122 and device area 118 whichinclude contacts (not shown) to the devices. The patterning may be by anacceptable process, such as by exposing the insulating layer 128 tolight when the insulating layer 128 is a photo-sensitive material or byetching using, for example, an anisotropic etch. If the insulating layer128 is a photo-sensitive material, the insulating layer 128 can bedeveloped after the exposure.

To form a first layer of metal lines 127 and vias 129, a seed layer (notshown) is formed over the insulating layer 128 and in openings throughthe insulating layer 128. In some embodiments, the seed layer is a metallayer, which may be a single layer or a composite layer comprising aplurality of sub-layers formed of different materials. In someembodiments, the seed layer comprises a titanium layer and a copperlayer over the titanium layer. The seed layer may be formed using, forexample, PVD or the like. A photo resist is then formed and patterned onthe seed layer. The photo resist may be formed by spin coating or thelike and may be exposed to light for patterning. The pattern of thephoto resist corresponds to the pattern of the metal lines 127. Thepatterning forms openings through the photo resist to expose the seedlayer. A conductive material is formed in the openings of the photoresist and on the exposed portions of the seed layer. The conductivematerial may be formed by plating, such as electroplating or electrolessplating, or the like. The conductive material may comprise a metal, likecopper, titanium, tungsten, aluminum, or the like. Then, the photoresist and portions of the seed layer on which the conductive materialis not formed are removed. The photo resist may be removed by anacceptable ashing or stripping process, such as using an oxygen plasmaor the like. Once the photo resist is removed, exposed portions of theseed layer are removed, such as by using an acceptable etching process,such as by wet or dry etching. The remaining portions of the seed layerand conductive material form the pattern of the metal lines 127 and vias129. The vias 129 are formed in openings through insulating layer 128to, e.g., the substrate 122 or device area 118.

A subsequent insulating layer 128 may then be deposited over the metallines 127 and vias 129 and the process repeated as needed to form amultilayer interconnect which forms a circuit and provides input/outputto the substrate 122 and device area 118. Optional metal pads 131 may beformed in a top most layer of the interconnect structure 126 in a mannersimilar to forming the metal lines 127.

Interconnect structure 126 also includes a seal ring structure 132Aformed in a similar manner as the other layers of the interconnectstructure 126, by alternating layers of metal lines and insulatingmaterials where the metal lines are coupled by vias. The seal ringstructure 132A may be included to help prevent delamination of thelayers in the interconnect structure 126. In some embodiments, anadditional seal ring structure 134A may be included. Seal ring structure134A may be formed in a similar manner as the other layers of theinterconnect structure 126 and seal ring structure 132A. The seal ringstructure 134A may be wider than seal ring structure 132A, narrower thanseal ring structure 132A, or the same width as seal ring structure 132A.

A passivation layer 138 may be formed over the interconnect structure126 and patterned to form openings therein, exposing a top metal layerof the interconnect structure 126 and exposing a top metal layer of theseal ring structure 132A and a top metal layer of the seal ringstructure 134A. Passivation layer 138 may be formed by the depositionand patterning of an insulating layer. In some embodiments, thepassivation layer 138 is formed of a polymer, which may be aphoto-sensitive material such as PBO, polyimide, BCB, or the like, thatmay be patterned using a lithography mask. In other embodiments, thepassivation layer 138 is formed of a nitride such as silicon nitride; anoxide such as silicon oxide, PSG, BSG, BPSG; or the like. Thepassivation layer 138 may be formed by spin coating, lamination, CVD,the like, or a combination thereof. Passivation layer 138 may be betweenabout 0.01 μm and 2 μm thick, such as about 0.9 μm thick. Otherthicknesses may be used.

The passivation layer 138 is patterned to form openings to exposeportions of the top metal layer of the interconnect structure 126. Thepatterning may be by an acceptable process, such as by exposing thepassivation layer 138 to light when the passivation layer 138 is aphoto-sensitive material or by etching using, for example, ananisotropic etch. If the passivation layer 138 is a photo-sensitivematerial, the passivation layer 138 can be developed after the exposure.

Seal rings structure 132A may be extended through and above thepassivation layer 138. A via 132B may be formed in the passivation layer138 and an overlying seal ring metal 132C may be formed over thepassivation layer 138. The resulting seal ring 132 may thereforecomprise seal ring structure 132A in interconnect structure 126, sealring via 132B through passivation layer 138, and seal ring metal 132C.In some embodiments, additional seal rings may be included. Inembodiments having one or more other seal rings, such as seal ring 134,such seal rings may similarly comprise the seal ring structure, such asseal ring structure 134A in the interconnect structure 126, a via, suchas seal ring via 134B through passivation layer 138, and a seal ringmetal, such as seal ring metal 134C. Seal ring unit 136 may comprise allof the seal rings surrounding the periphery of the die (e.g., seal ring132, seal ring 134, and so forth). Seal ring metal 132C and seal ringmetal 134C may form a continuous loop around the periphery of the die ina top down view.

Seal ring via 132B and 134B may be formed by a process similar to theformation of the metal lines and vias of interconnect structure 126,described above. The passivation layer 138 may be patterned to formopenings therein corresponding to the seal ring via 132B and seal ringvia 134B. A seed layer (not shown) may then be deposited over thepassivation layer and in the openings. A subsequent mask can bedeposited over the seed layer and patterned to create openings accordingto the seal ring metal 132C and seal ring metal 134C. The seal ring via132B and seal ring metal 132C can then be formed by depositing a metalmaterial such as copper, titanium, the like, or a combination thereof,formed by a plating process, such as electroless plating,electroplating, or the like on the seed layer first deposited in theopenings and continuing the plating until the seal ring metal 132C hasreached a desired height. The resulting seal ring metal 132C and sealring metal 134C may have a height h1 of about 0.1 μm to about 2.8 μm,such as about 2.8 μm. Other heights may be used for the seal ring metal132C and seal ring metal 134C. For example, in some embodiments, h1 maybe less than 0.1 μm or greater than 2.8 μm. Seal ring via 134B and sealring metal 134C may be formed simultaneously with seal ring via 132B andseal ring metal 132C. Following the formation of the seal ring 132 andseal ring 134, the mask may be removed by a suitable process, such as byashing, and the remaining seed layer stripped away.

Crack stoppers 130 may be formed around the die using processes andmaterials similar to those discussed above with respect to seal ring 132and seal ring 134, with the exception that the topmost layer of thecrack stoppers 130 are not formed in a continuous ring, but are formedas discontinuous metal layers (see, e.g., the example top profile ofcrack stoppers 130 in FIG. 2c ). In some embodiments, the crack stoppers130 may extend into interconnect structure 126 in discontinuous segmentswhich are aligned with the topmost layer of the crack stoppers 130. Insome embodiments, the portion of the crack stoppers 130 in interconnectstructure 126 may be formed in a continuous ring, similar to seal ringstructure 132 a, described above. Single or multiple rows of crackstoppers 130 may be used (see, e.g., FIG. 2c ), in some embodiments,including one, two, three, four, five, or six, rows and so forth.Additional rows of crack stoppers 130 may be used. Crack stoppers 130may be offset from one another to inhibit a crack from entering theinner part of die 112. For example, a crack which may start from anoutside edge of die 112 and proceed toward the inner part of die 112 maybe halted by one of the crack stoppers 130 and be stopped there insteadof encroaching into the inner part of die 112. Each crack stopper 130 isdesigned to end propagation of any such cracks, rather than allow thecrack to proceed past the crack stoppers 130 to the inner part of thedie 112. Crack stoppers 130 may appear in a top down view (see FIG. 2c )as round, square, rectangular, or any suitable shape.

A bond dielectric layer 140 may be formed over the passivation layer138. In some embodiments, bond dielectric layer 140 is an oxide layer,which may comprise silicon oxide. In other embodiments, bond dielectriclayer 140 comprises other silicon and/or oxygen containing materialssuch as SiON, SiN, or the like, and may be formed by any suitabledeposition technique. The bond dielectric layer 140 may be deposited toa thickness t2 of about 1.5 μm to about 7 μm, such as about 6 μm. Otherthicknesses may be used. The top surfaces of the seal ring metal 132Cand seal ring metal 134C may be covered by the bond dielectric layer140. The distance d3 between the top surfaces of the seal ring metal132C, for example, and the top surface of the bond dielectric layer 140may be about 1.2 μm to about 1.4 μm, such as about 1.3 μm. Otherdistances for distance d3 may be used.

Bond pads 142 are formed in bond dielectric layer 140, and may beelectrically coupled to device area 118 through metal lines and vias,including bond pad vias 144. Bond pads 142 may be formed of copper,aluminum, nickel, tungsten, or alloys thereof. The top surface of bonddielectric layer 140 and the top surfaces of bond pads 142 are levelwith each other, which is achieved through a planarization that isperformed during the formation of bond pads 142. The planarization maycomprise Chemical Mechanical Polish (CMP).

Bond pads 142 may be electrically connected to metal lines 127 and vias129 by a corresponding bond pad via 144 for each bond pad 142. In someembodiments, no bond pad vias 144 are formed between bond pads 142 andthe top metal of metal lines 127. Accordingly, the bond pads may be indirect physical contact with the top metal of the metal lines 127. Insome embodiments, one or more bond pad vias 144 may extend to the top ofthe bond dielectric layer 140 and the corresponding bond pad 142 may beomitted.

Bond pad vias 144 may be formed by patterning the bond dielectric layer140 to form openings which expose metal lines 127 or optional metal pads131 of interconnect structure 126. A metal material such as copper,titanium, the like, or a combination thereof, may be deposited in theopenings by a suitable deposition process, such as by a plating process,such as electroless plating, electroplating, or the like on an optionalseed layer first deposited in the openings. In some embodiments, afterformation of the bond pad vias 144, an additional layer of the bonddielectric layer 140 may be deposited over the bond pad vias 144, andthe bond dielectric layer 140 patterned again to provide openingscorresponding to the bond pads 142. Bond pads 142 may then be formed bydepositing a metal material such as copper, titanium, the like, or acombination thereof, formed by a plating process, such as electrolessplating, electroplating, or the like on an optional seed layer firstdeposited in the openings. In some embodiments, other depositionprocesses may be used instead of or in combination with a platingprocess, such as ALD, CVD, and the like. Excess material of the bondpads 142 may be removed by planarization, such as a CMP.

As shown in FIGS. 2a, 2b, and 2c , bond pads 142 are distributeduniformly or substantially uniformly (for example, with apattern-density variation smaller than about 10 percent). The(substantially) uniformly distributed bond pads 142 may be distributedthroughout an entirety or substantially the entirety of (for example,more than 90 or 95 percent) of die 112. However, rather than the(substantially) uniformly distributed bond pads 142 extending all theway to the edges of die 112, including over the seal ring unit 136, thedesign may be altered by removing the bond pads which would be over theseal ring unit 136 if the adjacent pattern were allowed to continue overthe seal ring unit 136. Furthermore, all or substantially all (such asmore than 90 percent) of bond pads 142 throughout the entire die 112 mayhave a same top-view shape, a same top-view size, and/or a same pitch.Accordingly, bond pads 142 may have a uniform pattern density throughoutdie 112, except for the area over the seal ring unit 136. In someembodiments, the distance dl may be between about 2 μm and about 10 μm,such as about 9 μm. Other distances for the pitch may be used. In someembodiments, the width d4 of the seal ring unit 136 and crack stop unit130 may be between about 20 μm and about 22 μm, such as about 22 μm. Insome embodiments, the width d4 of the seal ring unit 136 and crack stopunit 130 may be less than 20 μm, such as about 4 μm or may be greaterthan 22 μm, such as about 30 μm. Other distances may be used.

Removing the bond pads which would be over the seal ring unit 136produces keep out zone 150. Keep out zone 150 may extend further towardthe inner part of die 112 than the seal ring unit 136. For example, keepout zone 150 may include an area over crack stoppers 130. In someembodiments, keep out zone 150 may include an area over a portion ofmetal lines 127, vias 129, or optional metal pads 131 of interconnectstructure 126. A pattern design for bond pads 142 may initially includebond pads in keep out zone 150. The pattern design may then be alteredbefore manufacturing to remove bond pads 142 from the design where keepout zone 150 is located on die 112. For example, as illustrated in FIG.2b , keep out zone 150 corresponds to the location of the seal ring unit136 and extends into the inner part of die 112 over the crack stoppers130 and over a portion of a metal line 127 of interconnect structure126. In other embodiments, the keep out zone may be located in otherareas of the die (see, e.g., FIG. 7b and its description) which isdescribed in greater detail in discussing other embodiments, below. Thelocation of keep out zone 150 is based at least in part on where asecond die will be bonded to die 112. When the second die has the samefootprint dimensions, the keep out zone 150 will be located at theperiphery of the die, corresponding to the area of the seal ring unit136. When the second die has a smaller footprint, the keep out zone 150will be located at least in part in an interior part of the die.Examples of such embodiments are described in greater detail below withrespect to FIGS. 6 through 11.

In some embodiments, bond pads 142 may include a plurality of activemetal pads 142A and a plurality of dummy metal pads 142B. Dummy metalpads 142B do not have electrical functions. Active metal pads 142A maybe electrically connected to device area 118 through bond pad vias 144and interconnect structure 126. Dummy metal pads 142B are electricallydisconnected from devices in die 112, where the symbol “x” representsthat no electrical connection exists to connect dummy metal pads 142B todevice area 118. Accordingly, dummy metal pads 142B may be electricallyfloating. In some embodiments, active metal pads 142A and dummy metalpads 142B have the same top-view shape, the same top-view size, andcomprise the same material. Furthermore, active metal pads 142A anddummy metal pads 142B are formed simultaneously. In alternativeembodiments, active metal pads 142A and dummy metal pads 142B havedifferent top-view shapes and/or different top-view sizes.

Active metal pads 142A and dummy metal pads 142B may have a sametop-view shape and/or a same top-view size. Therefore, whether a bondpad 142 is used as an active metal pad 142A or a dummy metal pad 142B isdetermined by its electrical connection such as whether it is connectedto device area 118 or not. It should be understood that reference in thefigures to a bond pad 142 contemplates both an active metal pad 142A anddummy metal pad 142B depending on the die design. The designers whodesign die 112 may uniformly distribute bond pads 142 throughout die 112and/or wafer 100, and the electrical connections from device area 118 tobond pads 142 are made depending on the convenience in metal routing.For example, when an electrical connection needs to be made to connectto a part of device area 118, the most convenient bond pad 142, whichmay be the one nearest to the part of device area 118, or the one thatis easiest to route to, is selected as the active metal pad 142A. Thebond pads 142 that are not selected thus become dummy metal pads 142B.

FIG. 2c illustrates a top view of a corner portion of die 112. Althoughseal ring unit 136 and crack stoppers 130 would not be visible in thetop view, they have been illustrated for context and provided withdashed outside edges. The seal ring unit 136 comprising seal ring 132and seal ring 134 is illustrated to continue around the periphery of die112. All the bond pads 142 are contained within the seal ring unit 136.A keep out zone 150 for the seal ring unit 136 provides an area over theseal ring unit 136 which is free from bond pads 142. The keep out zone150 may continue around the entire edge of die 112. The top surface ofthe seal ring unit 136 is below the surface of the bond dielectric layer140. As such, the keep out zone 150 provides a bond-dielectric-layerarea free of metal features continuously extending from one edge of thekeep out zone to the other edges of the keep out zone for fusion bondingto another die while being unencumbered by any metal features. When thekeep out zone 150 is aligned to a keep out zone on another die, andbonded thereto, the bond yield rate is improved. The width d4 (see FIG.2b ) of the keep out zone 150 may be between about 20 μm and about 21.6μm, such as about 21.6 μm. Other distances may be used for the width ofthe keep out zone 150. The length of the keep out zone 150 may varybased on the size of the die which is to be bonded to die 112.

FIG. 2c also illustrates that some bond pads 142 may be active bond padshaving an active metal pad 142A which is coupled to a bond pad via 144(shown in phantom). Other bond pads 142 in the pattern may be dummy bondpads having a dummy metal pad 142B which is not coupled to a bond padvia 144.

FIGS. 3 through 4 c illustrate another die 212 in accordance with someembodiments. FIG. 3 illustrates a schematic top view of wafer 200 inaccordance with some embodiments. Wafer 200 includes dies 212 and theadjoining scribe lines 214 and 216, wherein scribe lines 214 and 216separate dies 212 from each other. Scribe lines 214 have longitudinaldirections parallel to the X direction, and scribe lines 216 havelongitudinal directions parallel to the Y direction, which isperpendicular to the X direction. In each of dies 212, there may be oneor more seal rings (e.g., shown as 236 in FIG. 4a ), wherein the outerboundaries of the seal rings define the outer boundaries of dies 212.Each of the scribe lines 214 is between and adjoining two rows of dies212, and each of the scribe lines 216 is between and adjoining twocolumns of dies 212. It is noted that wafer 200 is intended to be anexample only, and the sizes of dies 212, scribe lines 214 and 216, etc.may vary based on the die designs.

FIG. 4a illustrates a schematic perspective view of die 212. Die 212 inFIG. 4a may be singulated from wafer 200 or may still be intact withwafer 200. Seal ring unit 236 (shown in phantom) is disposed at aperiphery of die 212 under the surface of die 212 and may include one ormore distinct seal rings (described in greater detail below with respectto FIGS. 4b and 4c ). In some embodiments, die 212 comprises an array ofbond pads 242 set over and around a device area 218 of die 212. In someembodiments, the device area 218 may include the entire area of die 212within seal ring unit 236. In other embodiments, the device area 218 mayinclude a portion of the area of die 212 within seal ring unit 236, suchas illustrated in FIG. 4a . In some embodiments, the device area 218 mayinclude all the available bond pads 242 on the die or a subset of theavailable bond pads 242. Arrangements of bond pads 242 may be made in apattern other than an array pattern. Bond pads 242 may be sizedsimilarly or differently, depending on the design of the bond pads 242on die 212.

Die 212 may be a similar or identical device as die 112, in someembodiments and may have similar dimensions thereto, includingthicknesses of layers and so forth. In some embodiments, die 212 can bedifferent than die 112, and may include a logic device or memory devicesuch as memory cells including, and not limited to, Static Random AccessMemory (SRAM) cells, Dynamic Random Access Memory (DRAM) Cells,Magneto-Resistive Random Access Memory (MRAM) cells, or the like. Die212 may include other types of devices.

FIG. 4b illustrates a cross-sectional view of die 212. The cross-sectionof FIG. 4b is a portion of a cross-section taken along the line A-A ofFIG. 4c , however the details may be varied from one view to another forthe purposes of discussion. Die 212 includes substrate 222 which may bea semiconductor substrate, such as a silicon substrate, a silicongermanium substrate, a silicon carbon substrate, an III-V compoundsemiconductor substrate, or the like. A device area 218 is formed at thesurface or inside substrate 222. Device area 218 may comprise active orpassive devices, such as transistors, resistors, capacitors, diodes, andthe like. In some embodiments, device area 218 may comprise anencapsulated die.

An interconnect structure 226 may be formed over the substrate 222.Interconnect structure 226 may include insulating layers 228, such as aninter-layer dielectric (ILD) and/or inter-metal dielectric layers (IMD)and conductive features (e.g., metal lines 227, vias 229, and optionalmetal pads 231) formed in alternating layers over substrate 222 usingprocesses and materials such as those described above with respect tointerconnect structure 126 of FIG. 2b , which are not repeated.Interconnect structure 226 may connect various active and/or passivedevices in device area 218 of substrate 222 to form functional circuits.

The interconnect structure 226 also includes a seal ring structure 232Aformed in a similar manner as the other layers of the interconnectstructure 226, by alternating layers of metal lines and insulatingmaterials where the metal lines are coupled by vias. The seal ringstructure 232A may be included to help prevent delamination of thelayers in the interconnect structure 226. In some embodiments, anadditional seal ring structure 234A may be included. Seal ring structure234A may be formed in a similar manner as the other layers of theinterconnect structure 226 and seal ring structure 232A. The seal ringstructure 234A may be wider than seal ring structure 232A, narrower thanseal ring structure 232A, or the same width as seal ring structure 232A.

A passivation layer 238 may be formed over the interconnect structure226 and patterned to form openings therein, exposing a top metal layerof the interconnect structure 226 (or optional metal pad 231) andexposing a top metal layer of the seal ring structure 232A and a topmetal layer of the seal ring structure 234A. Passivation layer 238 maybe formed using processes and materials such as those discussed abovewith respect to passivation layer 138, which are not repeated.

Seal ring structure 232A may be extended through and above thepassivation layer 238. A via 232B may be formed in the passivation layer238 and an overlying seal ring metal 232C may be formed over thepassivation layer 238. The resulting seal ring 232 may thereforecomprise seal ring structure 232A in interconnect structure 226, sealring via 232B through passivation layer 238, and seal ring metal 232C.In some embodiments, additional seal rings may be included. Inembodiments having another seal ring, such as seal ring 234, such sealrings may similarly comprise the seal ring structure, such as seal ringstructure 234A in the interconnect structure 226, a via, such as via234B through passivation layer 238, and a seal ring metal, such as sealring metal 234C. Seal ring unit 236 may comprise all of the seal ringssurrounding the periphery of the die (e.g., seal ring 232, seal ring234, and so forth). Seal ring metal 232C and seal ring metal 234C mayform a continuous loop around the periphery of the die in a top downview.

Seal ring via 232B or seal ring via 234B may be formed using processesand materials such as those discussed above with respect to seal ringvia 132B and seal ring via 134B, which are not repeated. Similarly, sealring metal 232C and 234C may be formed using processes and materialssuch as those discussed above with respect to seal ring metal 132C andseal ring metal 134C, which are not repeated.

Crack stoppers 230 may be formed around the die. Crack stoppers 230 maybe formed using processes and materials such as described above withrespect to crack stoppers 130 which are not repeated.

A bond dielectric layer 240 may be formed over the passivation layer238. In some embodiments, bond dielectric layer 240 is an oxide layer,which may comprise silicon oxide. In other embodiments, bond dielectriclayer 240 comprises other silicon and/or oxygen containing materialssuch as SiON, SiN, or the like. Bond pads 242 are formed in bonddielectric layer 240, and may be electrically coupled to device area 218through metal lines and vias, including bond pad vias 244. Bond pads 242may be formed of copper, aluminum, nickel, tungsten, or alloys thereof.The top surfaces of the seal ring metal 232C and seal ring metal 234Cmay be covered by the bond dielectric layer 240. The top surface of bonddielectric layer 240 and the top surfaces of bond pads 242 are levelwith each other, which is achieved through a planarization that isperformed during the formation of bond pads 242. The planarization maycomprise a CMP process.

Bond pads 242 may be electrically connected to metal lines 227 and vias229 by a corresponding bond pad via 244 for each bond pad 242. In someembodiments, no bond pad vias 244 are formed between bond pads 242 andthe top metal of metal lines 227. Accordingly, the bond pads may be indirect physical contact with the top metal of the metal lines 227. Insome embodiments, one or more bond pad vias 244 may extend to the top ofthe bond dielectric layer 240 and the corresponding bond pad 242 may beomitted. Bond pad vias 244 and bond pads 242 may be formed usingprocesses and materials such as those discussed above with respect tothe bond pad vias 144 and bond pads 142 of FIG. 2b , which are notrepeated.

In some embodiments, bond pads 242 may include a plurality of activemetal pads 242A and a plurality of dummy metal pads 242B, similar to theactive metal pads 142A and dummy metal pads 142B of FIG. 2 b.

Referring now to FIG. 4c , FIG. 4c illustrates a top view of a cornerportion of die 212. The seal ring unit 236 comprising seal ring 232 andseal ring 234 is illustrated to continue around the periphery of die212. All the bond pads 242 are contained within the seal ring unit 236.A keep out zone 250 for the seal ring unit 236 provides an area over theseal ring unit 236 which is free from bond pads 242. Keep out zone 250is similar in size and shape as keep out zone 150 of die 112. Keep outzone 250 is sized to be aligned to keep out zone 150 of die 112 and hasa dielectric bond area which continuously extends from one edge of thekeep out zone to the other edges of the keep out zone for fusion bondingto another die while being unencumbered by any metal features. The topsurface of the seal ring unit 236 is below the surface of the bonddielectric layer 240. As such, the keep out zone 250 provides adielectric bond area for fusion bonding to another die, such as die 112.Keep out zone 250 may be located using similar processes as describedabove with respect to keep out zone 150 of FIGS. 2b and 2 c.

Referring to FIG. 5, FIG. 5 illustrates a cross-section that includesdie 112 bonded to die 212 to form die package 213. Bonding can bewafer-to-wafer where both wafers are directly bonded together,chip-to-chip where two singulated chips (or dies) are directly bondedtogether, or chip-to-wafer where one or more chips (or dies) aredirectly bonded together, wherein the dielectric layers of one die arefusion bonded to another die and the metal layers of one die and anotherdie are bonded together without using any eutectic material, such assolder. For example, in a wafer-to-wafer bonding, the bonding of wafer100 to wafer 200 is through hybrid bonding, wherein dies 112 are bondedto dies 212 prior to singulation. In the hybrid bonding of wafers 100and 200, bond dielectric layer 140 is bonded to bond dielectric layer240 through fusion bonding, and the metal of bond pads 142 are bonded tothe metal of bond pads 242 through metal-to-metal bonding. Chip-to-chipor chip-to-wafer bonding proceeds similarly, except for the method usedfor aligning the chips or chips and wafer.

The bonding may include a pre-bonding and an annealing. During thepre-bonding, a small pressing force is applied to press wafers 100 and200 against each other. The pre-bonding may be performed at the roomtemperature (for example, between about 21° C. to about 25° C.),although higher temperatures may be used. After the pre-bonding, bonddielectric layers 140 and 240 are bonded to each other. The bondingstrength is improved in a subsequent annealing step, in which the bondedwafers 100 and 200 are annealed at a temperature between about 300° C.and about 400° C., for example.

The annealing may be performed for a period of time between about 1 hourand 2 hours. When temperature rises, the OH bond in bond dielectriclayer 140 and bond dielectric layer 240 break to form strong Si—O—Sibonds, and hence wafers 100 and 200 are bonded to each other throughfusion bonds (and through Van Der Waals force). In addition, during theannealing, the metal (such as copper) in bond pads 142 and bond pads 242diffuse into each other, so that metal-to-metal bonds are also formed.Hence, the resulting bonds between wafers 100 and 200 are hybrid bonds.After the bonding, the bonded wafer 100 and 200 may be sawed intopackages, with each of the packages including die 112 bonded to die 212.

As shown in FIG. 5, bond pads 142 and bond pads 242 are bonded to eachother with a one-to-one correspondence. In some embodiments, each ofbond pads 142 has a corresponding bond pad 242 to bond to, and each ofbond pads 242 has a corresponding bond pad 142 to bond to. Active metalpads 142A are bonded to active metal pads 242A, and dummy metal pads142B are bonded to dummy metal pads 242B. In some embodiments, dummymetal pads may be bonded to active metal pads. For example, dummy metalpad 142B may be bonded to active metal pad 242A. In some embodiments, amisalignment might occur in the pattern or in the alignment of one waferto the other and a portion of one or more of bond pads 142 may slightlyoverhang or underhang a corresponding one of bond pads 242.

Removing dummy metal pads 142B and 242B from over the seal ring units136 and 236 provides for a more reliable bonding to the bond dielectriclayers 140 and 240, thereby improving bonding yield and creating bondsless prone to bond failure. This result is unexpected because includingdummy metal pads in this area can provide a more uniform pattern densitywhich would result in a more level surface following planarization.

The embodiments discussed above apply when the die sizes are the samesuch that the edges of the two dies are aligned. Similar processes canbe used to provide bonding with dies of two different sizes. FIGS. 6through 7 c illustrate another die 312 in accordance with someembodiments. FIG. 6 illustrates a schematic top view of wafer 300 inaccordance with some embodiments. Wafer 300 includes dies 312 and theadjoining scribe lines 314 and 316 similar to scribe lines 114 and 116of FIG. 1.

FIG. 7a illustrates a schematic perspective view of die 312. Die 312 inFIG. 7a may be singulated from wafer 300 or may still be intact withwafer 300. Seal ring unit 336 is disposed at a periphery of die 312 andmay include one or more distinct seal rings (described in greater detailbelow with respect to FIGS. 7b and 7c ). In some embodiments, die 312comprises an array of bond pads 342 set over and around a device area318 of die 312. In some embodiments, the device area 318 may include theentire area of die 312 within seal ring unit 336. In other embodiments,the device area 318 may include a portion of the area of die 312 withinseal ring unit 336, such as illustrated in FIG. 7a . In someembodiments, the device area 318 may include all the available bond pads342 on the die or a subset of the available bond pads 342. Arrangementsof bond pads 342 may be made in a pattern other than an array pattern.Bond pads 342 may be sized similarly or differently, depending on thedesign of the bond pads 342 on die 312.

Die 312 may be a similar device as die 112, in some embodiments, and mayhave similar dimensions thereto, including thicknesses of layers and soforth. In some embodiments, die 312 may include a logic device or memorydevice such as memory cells including, and not limited to, Static RandomAccess Memory (SRAM) cells, Dynamic Random Access Memory (DRAM) Cells,Magneto-Resistive Random Access Memory (MRAM) cells, or the like. Die312 may include other types of devices.

FIG. 7b illustrates a cross-sectional view of die 312. The cross-sectionof FIG. 7b is a portion of a cross-section taken along the line A-A ofFIG. 7c , however the details may be varied from one view to another forthe purposes of discussion. Die 312 includes a substrate 322, similar tosubstrate 122 and device area 318, similar to device area 118.

An interconnect structure 326 may be formed over substrate 322.Interconnect structure 326 may include insulating layers 328 andconductive features (e.g., metal lines 327, vias 329, and optional metalpads 331). Interconnect structure 326 may connect various active and/orpassive devices in device area 318 of substrate 322 to form functionalcircuits. Interconnect structure 326 may be formed using materials andprocesses similar to those discussed above with respect to interconnectstructure 126 of FIG. 2b , which are not repeated.

Interconnect structure 326 also includes a seal ring structure 332A,similar to seal ring structure 132A of FIG. 2b . Other seal ringstructures, such as seal ring structure 334A may also be formed ininterconnect structure 326. Seal ring structure 332A and seal ringstructure 334A may be formed in a similar manner as the other layers ofthe interconnect structure 326.

A passivation layer 338 may be formed over the interconnect structure326 and patterned to form openings therein, exposing a top metal layerof the interconnect structure 326 (or optional metal pad 331) andexposing a top metal layer of the seal ring structure 332A and a topmetal layer of the seal ring structure 334A. Passivation layer 338 maybe formed using processes and materials such as those discussed abovewith respect to passivation layer 138, which are not repeated.

Seal ring structure 332A may be extended through and over thepassivation layer 338. A via 332B may be formed in the passivation layer338 and an overlying seal ring metal 332C may be formed over thepassivation layer 338. The resulting seal ring 332 may thereforecomprise seal ring structure 332A in interconnect structure 326, sealring via 332B through passivation layer 338, and seal ring metal 332C.In some embodiments, additional seal rings may be included. Inembodiments having additional seal rings, such as seal ring 334, suchseal rings may similarly comprise the seal ring structure, such as sealring structure 334A in the interconnect structure 326, a via, such asvia 334B through passivation layer 338, and a seal ring metal, such asseal ring metal 334C. Seal ring unit 336 may comprise all of the sealrings surrounding the periphery of the die (e.g., seal ring 332, sealring 334, and so forth). Seal ring metal 332C and seal ring metal 334Cmay form a continuous loop around the periphery of the die in a top downview.

Seal ring via 332B and seal ring via 334B may be formed using processesand materials such as those discussed above with respect to seal ringvia 132B and seal ring via 134B, which are not repeated. Similarly, sealring metal 332C and seal ring metal 334C may be formed using processesand materials such as those discussed above with respect to seal ringmetal 132C and seal ring metal 134C, which are not repeated.

Crack stoppers 330 may be formed around the die. Crack stoppers 430 maybe formed using processes and materials such as described above withrespect to crack stoppers 130 which are not repeated.

A bond dielectric layer 340 may be formed over the passivation layer 338and seal ring unit 336. Bond dielectric layer 340 may be formed usingprocesses and materials similar to those discussed above with respect tobond dielectric layer 140, which are not repeated.

Bond pads 342 are formed in bond dielectric layer 340, and may beelectrically coupled to device area 318 through metal lines and vias,including bond pad vias 344. Bond pads 342 and bond pad vias 344 may beformed using processes and materials such as those discussed above withrespect to bond pads 142 and bond pad vias 144, which are not repeated.Bond pads 342 may include a plurality of active metal pads 342A and aplurality of dummy metal pads 342B, similar to the active metal pads142A and dummy metal pads 142B of FIG. 2 b.

Still referring to FIG. 7b , the dummy metal pads 342B can be removedfrom the design pattern where the seal ring from the die to be bondedwill interface with die 312. Keep out zone 350 illustrates an area ofthe bond dielectric layer 340 which has a surface comprising acontinuous dielectric interface layer which is free from bond pads 342.As illustrated in FIG. 7b , dummy metal pads 342B may be included overthe seal ring unit 336 as part of the substantially uniform pattern ofbond pads 342. In other embodiments, the dummy metal pads 342B areoptional and may be omitted from over the seal ring unit 336. Otherdummy metal pads 342B may be interspersed throughout the design pattern,depending on whether a bond pad via 344 is used to couple the bond pad342 to a metal feature in the interconnect layer 326. In someembodiments, such as illustrated in FIG. 7b , some of the bond pads 342between keep out zone 350 and the seal ring unit 336 may be active metalpads 342A and may be used for bonding to other devices, or for formingconnectors thereon. In other embodiments not specifically illustrated,all bond pads 342 between the keep out zone 350 and seal ring unit 336may be dummy metal pads 342B.

An area of the die 312 will interface with a keep out zone of anotherdie which will be bonded to die 312. Removing bond pads 342 in this areawhich will bond with the other die's keep out zone produces keep outzone 350. Keep out zone 350 may include a portion of bond dielectriclayer 340 in an inner part of die 312, such as areas over a portion ofmetal lines 327, vias 329, or optional metal pads 331 of interconnectstructure 326. Keep out zone 350 may also include a portion of bonddielectric layer 340 over seal ring unit 336 (see, e.g., FIG. 7c ). Apattern design for bond pads 342 may initially include bond pads in keepout zone 350. The pattern design may then be altered beforemanufacturing to remove bond pads 342 from the design where the keep outzone 350 is located on die 312. For example, as illustrated in FIG. 7b ,keep out zone 350 corresponds in part to the location of where a keepout zone for another die will be bonded. The location of keep out zone350 is thus based on where a second die will be bonded to die 312. Whenthe second die has smaller footprint dimensions than die 312, the keepout zone 350 will be located at least in part at an inner portion ofbond dielectric layer 340. In some embodiments, one or more edges of thetwo dies may be aligned so that part of the keep out zone 350 is overseal ring unit 336 and part of keep out zone 350 is over an interiorpart of die 312. In some embodiments, the bond pad vias 344 whichcorrespond to the bond pads 342 which are removed, may also be removedfrom the design, while in other embodiments, some may remain in thedesign. Some embodiments may have a combination where some of the bondpad vias 344 remain and some are removed, such as illustrated in FIG. 7b.

Referring now to FIG. 7c , FIG. 7c illustrates a top view of a cornerportion of die 312. Although seal ring unit 336 and crack stoppers 330would not be visible in the top view, they have been illustrated forcontext and provided with dashed outside edges. A keep out zone 350provides an area over die 312 which is free from bond pads 342. The keepout zone 350 may continue along an edge of die 312 over a portion of theseal ring unit 336, in some embodiments. In other embodiments, the keepout zone 350 may be completely within the seal ring unit 336 outline,such that the keep out zone 350 does not overlap any of the seal ringunit 336. The top surface of the seal ring unit 336 is below the surfaceof the bond dielectric layer 340. As such, the keep out zone 350provides a dielectric bond area continuously extending from one edge ofthe keep out zone to the other edges of the keep out zone for fusionbonding to the keep out zone of another die while being unencumbered byany metal features. When the keep out zone 350 is aligned to a keep outzone on another die, and bonded thereto, the bond yield rate isimproved. The keep out zone 350 provides a dielectric bond area forfusion bonding to another die, such as die 412 (discussed below withrespect to FIGS. 10a through 10c ).

FIGS. 8 through 10 c illustrate another die 412 in accordance with someembodiments. FIG. 8 illustrates a schematic top view of wafer 400 inaccordance with some embodiments. Wafer 400 includes dies 412 and theadjoining scribe lines 414 and 416 similar to scribe lines 114 and 116of FIG. 1. The foot print of die 412 may be designed to have a smallerarea than the foot print of die 312. In some embodiments, die 412 mayhave a dimension in common with the foot print of die 312 (e.g., havingthe same width, but different lengths, or vice-versa), while in otherembodiments, die 412 may have a smaller width and length than that ofdie 312.

FIG. 9a illustrates a schematic perspective view of die 412. Die 412 inFIG. 9a may be singulated from wafer 400 or may still be intact withwafer 400. Seal ring unit 436 (shown in phantom) is disposed at aperiphery of die 412 under the surface of die 412 and may include one ormore distinct seal rings (described in greater detail below with respectto FIGS. 9b and 9c ). In some embodiments, die 412 comprises an array ofbond pads 442 set over and around a device area 418 of die 412. In someembodiments, the device area 418 may include the entire area of die 412within seal ring unit 436. In other embodiments, the device area 418 mayinclude a portion of the area of die 412 within seal ring unit 436, suchas illustrated in FIG. 9a . In some embodiments, the device area 418 mayinclude all the available bond pads 442 on the die or a subset of theavailable bond pads 442. Arrangements of bond pads 442 may be made in apattern other than an array pattern. Bond pads 442 may be sizedsimilarly or differently, depending on the design of the bond pads 442on die 412.

Die 412 may be a similar device as die 112, in some embodiments, and mayhave similar dimensions thereto, including thicknesses of the layers andso forth. Die 412 has a smaller footprint than die 312 in at least onelateral dimension, such that, when bonded to die 312, die 312 overlapsdie 412 by one or more edges. Die 412 may have first width, e.g., in theX direction of w3, which may be between about 2000 μm and about 26000μm, such as about 10000 μm. Die 412 may have second width (or length),e.g., in the Y direction of w4, which may be between about 2000 μm andabout 33000 μm, such as about 10000 μm. Other dimensions for die 412 maybe used. In some embodiments, die 412 may include a logic device ormemory device such as memory cells including, and not limited to, StaticRandom Access Memory (SRAM) cells, Dynamic Random Access Memory (DRAM)Cells, Magneto-Resistive Random Access Memory (MRAM) cells, or the like.Die 412 may include other types of devices.

FIG. 9b illustrates a cross-sectional view of die 412. The cross-sectionof FIG. 9b is a portion of a cross-section taken along the line A-A ofFIG. 9c , however the details may be varied from one view to another forthe purposes of discussion. Die 412 includes a substrate 422, similar tosubstrate 122 and device area 418, similar to device area 118.

An interconnect structure 426 may be formed over substrate 422.Interconnect structure 426 may include insulating layers 428 andconductive features (e.g., metal lines 427, vias 429, and optional metalpads 431). Interconnect structure 426 may connect various active and/orpassive devices in device area 418 of substrate 422 to form functionalcircuits. Interconnect structure 426 may be formed using materials andprocesses similar to those discussed above with respect to interconnectstructure 126 of FIG. 2b , which are not repeated.

Interconnect structure 426 also includes a seal ring structure 432A,similar to seal ring structure 132A of FIG. 2b . Other seal ringstructures, such as seal ring structure 434A may also be formed ininterconnect structure 426. Seal ring structure 432A and seal ringstructure 434A may be formed in a similar manner as the other layers ofthe interconnect structure 426.

A passivation layer 438 may be formed over the interconnect structure426 and patterned to form openings therein, exposing a top metal layerof the interconnect structure 426 and exposing a top metal layer of theseal ring structure 432A and a top metal layer of the seal ringstructure 434A. Passivation layer 438 may be formed using processes andmaterials such as those discussed above with respect to passivationlayer 138, which are not repeated.

Seal ring structure 432A may be extended through and over thepassivation layer 438. A via 432B may be formed in the passivation layer438 and an overlying seal ring metal 432C may be formed over thepassivation layer 438. The resulting seal ring 432 may thereforecomprise seal ring structure 432A in interconnect structure 426, sealring via 432B through passivation layer 438, and seal ring metal 432C.In some embodiments, additional seal rings may be included, such as sealring 434, which has similar layers as seal ring 432. Seal ring unit 436may comprise all of the seal rings surrounding the periphery of the die(e.g., seal ring 432, seal ring 434, and so forth). Seal ring metal 432Cand seal ring metal 434C may form a continuous loop around the peripheryof the die in a top down view.

Seal ring via 432B and seal ring via 434B may be formed using processesand materials such as those discussed above with respect to seal ringvia 132B and seal ring via 134B, which are not repeated. Similarly, sealring metal 432C and seal ring metal 434C may be formed using processesand materials such as those discussed above with respect to seal ringmetal 132C and seal ring metal 134C, which are not repeated.

Crack stoppers 430 may be formed around the die. Crack stoppers 430 maybe formed using processes and materials such as described above withrespect to crack stoppers 130 which are not repeated.

A bond dielectric layer 440 may be formed over the passivation layer 438and seal ring unit 436. Bond dielectric layer 440 may be formed usingprocesses and materials similar to those discussed above with respect tobond dielectric layer 140, which are not repeated.

Bond pads 442 are formed in bond dielectric layer 440, and may beelectrically coupled to device area 418 through metal lines and vias,including bond pad vias 444. Bond pads 442 and bond pad vias 444 may beformed using processes and materials such as those discussed above withrespect to bond pads 142 and bond pad vias 144, which are not repeated.Bond pads 442 may include a plurality of active metal pads 442A and aplurality of dummy metal pads 442B, similar to the active metal pads142A and dummy metal pads 142B of FIG. 2 b.

Still referring to FIG. 9b , the dummy metal pads 442B can be removedfrom the design pattern in bond dielectric layer 440 where the seal ringunit 436 of die 412 is located. Bond dielectric layer 440 will fusionbond with bond dielectric layer 340 of die 312 in this area. Keep outzone 450 illustrates the area of the bond dielectric layer 440 which isfree from bond pads 442. Providing a design of a die, such as die 412 toinclude keep out zone 450 may be done in a manner similar to thatdescribed above with respect to FIG. 2b , which is not repeated. Otherdummy metal pads 442B may be interspersed throughout the design pattern,depending on whether a bond pad via 444 is used to couple the bond pad442 to a metal feature in interconnect structure 426.

Referring now to FIG. 9c , FIG. 9c illustrates a top view of a cornerportion of die 412. Although the seal ring unit 436 and crack stoppers430 would not be visible in the top view, they have been illustrated forcontext and provided with dashed outside edges. The seal ring unit 436comprising seal ring 432 and seal ring 434 is illustrated to continuearound the periphery of die 412. All the bond pads 442 are containedwithin the seal ring unit 436. Keep out zone 450 for the seal ring unit436 provides an area over the seal ring unit 436 which is free from bondpads 442. Keep out zone 450 is similar to keep out zone 150 of FIG. 2c ,and includes a continuous dielectric surface layer from one edge of keepout zone 450 to the other edges of keep out zone 450, which is free frombond pads 442. The top surface of the seal ring unit 436 is below thesurface of the bond dielectric layer 440. As such, the keep out zone 450provides a dielectric bond area for fusion bonding to another die, suchas die 312.

Referring to FIG. 10a , a schematic perspective view of die 312 bondedto die 412 is shown. Die 412 has been flipped over and bondedface-to-face with die 312. Seal ring unit 436 of die 412 is shown inphantom and would not be visible. As seen in FIG. 10a , die 412 has thesame length as die 312, but is narrower than die 312. Die 412 has beenpositioned on die 312 so that two of the edges of each die are alignedwith a corresponding edge of the opposite die. In other examples, die412 may be positioned on die 312 so that a third edge of each die isaligned with a corresponding edge of the opposite die. In otherexamples, die 412 may be smaller in both length and width than die 312and may be positioned on die 312 such that zero or one edge of each dieis aligned with a corresponding edge of the opposite die.

Referring now to FIG. 10b , FIG. 10b illustrates a cross-section thatincludes die 312 bonded to die 412 to form die package 413. Bonding canbe chip-to-chip where two singulated chips (or dies) are directly bondedtogether or chip-to-wafer where one or more chips (or dies) are directlybonded together to a wafer (e.g., wafer 300). The direct bonding may beaccomplished by hybrid bonding, which an example process is describedabove with respect to FIG. 5.

As shown in FIG. 10b , bond pads 342 and bond pads 442 are bonded toeach other with a one-to-one correspondence. In some embodiments, eachof bond pads 342 has a corresponding bond pad 442 to bond to, and eachof bond pads 442 has a corresponding metal pad 342 to bond to. In someembodiments, bond pads 342 which are outside the footprint of die 412(exposed from die 412) may remain unbonded. In some embodiments, bondpads 342 outside the footprint of die 412 may be bonded to another die(not shown) using similar processes and materials as the bonding to die412. Active metal pads 342A are bonded to active metal pads 442A, anddummy metal pads 342B are bonded to dummy metal pads 442B. In someembodiments, dummy metal pads of one die or the other may be bonded toactive metal pads of the opposite die. For example, dummy metal pad 342Bmay be bonded to active metal pad 442A. In some embodiments, a slightmisalignment might occur in the pattern or in the alignment of one waferto the other and a portion of one or more of bond pads 342 may slightlyoverhang or underhang a corresponding one of bond pads 442.

FIG. 10c illustrates a top view of a corner portion of die 312 bonded todie 412. As shown in FIG. 10c , the keep out zones 350 and 450 arealigned to provide a direct fusion bonding of the bond dielectric layer340 to the bond dielectric layer 440 in that area. As shown in FIG. 10c, in some embodiments, an edge of die 312 may be aligned to an edge ofdie 412. Die 412 is flipped over and bonded to die 312. The seal ringunit 436, crack stoppers 430 and bond pads 442 would not be visible, buthave been illustrated for context.

Referring to FIG. 11, FIG. 11 illustrates another embodiment where a die312 is bonded to die 412 having a smaller footprint (see FIG. 9a and itsaccompanying description), similar to the view of FIG. 10c . As shown inFIG. 11, two or more adjacent edges of die 412 are not aligned tocorresponding adjacent edges of die 312. In some embodiments, some edgesmay be aligned while in other embodiments, none of the edges arealigned.

FIGS. 12 through 13 c illustrate another embodiment for a seal ringdesign which includes bond pads over the seal ring unit, but couples thebond pads over the seal ring unit to the seal ring. Referring to FIG.12, FIG. 12 illustrates a wafer 500 having dies 512 disposed thereon.Wafer 500 and dies 512 are substantially similar to the wafer 100 anddies 112, except as described below. Accordingly, the details for dies512 are omitted for the sake of brevity. Referring to FIG. 13a , die 512contains similar features and structures as dies 112 including a sealring unit 536, device area 518, and bond pads 542. In addition, die 512includes additional ring-like bond pads 552. Ring-like bond pads 552include a ring-like structure disposed over and coupled to each of theseal ring unit 536.

Referring to FIG. 13b , a cross-section of die 512 is illustrated inaccordance with some embodiments. Die 512 contains similar features andstructures as die 112, including substrate 522, interconnect structure526, passivation layer 538, bond dielectric layer 540, and a seal ringunit 536 which may include one or more seal rings 532 and 534, eachincluding a seal ring structure 532A (and 534A) in the interconnectstructure 526, a seal ring via 532B (and 534B), and seal ring metal 532C(and 534C). Die 512 may also include crack stoppers 530. Die 512 alsoincludes bond pad 542, including active metal pads 542A coupled to ametal feature in the interconnect structure 526 by bond pad vias 544 anddummy metal pads 542B which are not coupled to the interconnectstructure 526. In addition to these common features, as noted above, die512 includes one or more ring-like bond pads 552 coupled to each of theseal ring structures in seal ring unit 536. The ring-like bond pads 552may be formed in a continuous ring around the periphery of die 512disposed over the seal ring structures. The ring-like bond pads 552 arecoupled to the seal ring by one or more bond pad vias 554. In someembodiments, bond pad vias 554 may be disposed at regular intervalsaround the ring-like bond pads 552. In other embodiments, the one ormore bond pad vias 554 may also be ring-like, and are formed in a trenchall around the periphery of die 512. An inactive zone 551 is located atthe periphery of die 512. Inactive zone 551 is similar to keep out zone150 of FIG. 2b , except that ring-like bond pads 552, bond pad vias 554,and optional dummy metal pads 542/542B may be included. Althoughring-like bond pads 552 are inactive, they are coupled to the underlyingseal ring unit 536. In some embodiments, other dummy metal pads 542/542Bwhich are not coupled to any underlying features may also be included ininactive zone 551.

In some embodiments, bond pad vias 554 may be formed in a manner similarto the bond pad vias 544, which is not repeated. In other embodiments,bond pad vias 554 may be formed in a separate processing step than theforming of the bond pad vias 544. For example, a first resist layer canbe patterned to expose portions of dielectric bond layer 540corresponding to bond pad vias 554. Openings in dielectric bond layer540 may then be formed to expose seal ring unit 536. A conductivematerial may then be deposited in the openings to form bond pad vias554. The process can be repeated using a second resist layer to formbond pad vias 544. The order for forming bond pad vias 544 and bond padvias 554 can be reversed. In some embodiments, the openings for each ofbond pad vias 544 and bond pad vias 554 can be separately formed, asdescribed above, and then the conductive material depositedsimultaneously.

Ring-like bond pad 552 may be formed in a manner similar to the bondpads 542, which is not repeated. By forming a bond pads over the sealring, which are attached to the seal ring, the bonding of die 512 toanother die is improved over having dummy bond pads alone.

Inactive zone 551 may be created in a manner similar to that of keep outzone 150 of FIG. 2b . A pattern design for bond pads 542 may initiallyinclude bond pads in inactive zone 551. The pattern design may then bealtered to remove bond pads 542 from the design where inactive zone 551is located on die 512. For example, as illustrated in FIG. 13b ,inactive zone 551 corresponds to the location of the seal ring unit 536and extends into the inner part of die 512 over the crack stoppers 530and over a portion of a metal line of interconnect structure 526. Inother embodiments, the inactive zone may be located in other areas ofthe die (see, e.g., FIG. 7b ). The location of inactive zone 551 isbased on where a second die will be bonded to die 512. When the seconddie has the same footprint dimensions, inactive zone 551 will be locatedat the periphery of the die, corresponding to the area of seal ring unit536. When the second die has a smaller footprint, inactive zone 551 willbe located at least in part in an interior part of the die 512. Examplesof such embodiments are described in greater detail below with respectto FIGS. 15 and 16.

Referring now to FIG. 14, die 512 is bonded to a similarly formed die612, in accordance with some embodiments. Die 612 has similar featuresas die 512 with corresponding elements labelled similarly, except thatthe elements begin with a “6” instead of a “5.” Die 512 and die 612 maybe bonded as a wafer-to-wafer, chip-to-chip, or chip-to-wafer process.Die 512 and die 612 may be hybrid bonded to each other, for example,using a hybrid bonding process such as described above with respect toFIG. 5.

Referring now to FIG. 15, die 512 is bonded to another die 712, inaccordance with some embodiments. Die 712 has similar features as die512 with corresponding elements labelled similarly, except that theelements begin with a “7” instead of a “5.” In some embodiments, die 712may be formed using processes consistent with those discussed above withrespect to die 312, except for the inclusion of a keep out zone. Similarto that described above with respect to FIG. 10b , however, die 512 issmaller than die 712 and at least one of the edges of the dies 712 and512 are not aligned in top view (see, e.g., FIGS. 10c and 11). Similarto die 312 discussed above, the dummy metal pads 742B disposed over theseal ring unit 736 may be omitted in some embodiments. Die 712 may alsoinclude ring-like bond pads 752, similar to ring-like bond pads 552, asdiscussed above. Die 512 and die 712 may be hybrid bonded to each other,for example, using a hybrid bonding process such as described above withrespect to FIG. 5. Ring-like bond pads 752 in die 712 interfacing withinactive zone 551 of die 512 may be bonded to the ring-like bond pads552 of die 512.

Referring now to FIG. 16, die 512 is bonded to another die 812, inaccordance with some embodiments. Die 812 has similar features as die512 with corresponding elements labelled similarly, except that theelements begin with an “8” instead of a “5.” Die 812 may be formed to besubstantially similar to die 712, except that instead of a keep outzone, die 812 includes inactive zone 851 including ring-like bond pads852 (and bond pad vias 854) aligned with the ring-like bond pads 552 aswell as ring-like bond pads 852 (and bond pad vias 854) aligned with andcoupled to the seal ring 832 and seal ring 834 of seal ring unit 836.Ring-like bond pads 852 (and bond pad vias 854) may be formed usingprocesses and materials similar to those discussed above with respect toring-like bond pads 552 (and bond pad vias 554). Die 512 and die 812 maybe hybrid bonded to each other, for example, using a hybrid bondingprocess such as described above with respect to FIG. 5. One of skillwill understand that the different features of FIGS. 15 and 16 may becombined in another embodiment.

FIG. 17 illustrates a flow diagram for altering a bond pad design toaccommodate a keep out area, in accordance with some embodiments. Instep 1710, a substantially uniform bond pad layout for a first die iscreated. A substantially uniform bond pad layout can include a layout ofbond pads with no more than about 10% variation in pattern and/or bondpad sizes. At step 1720, an interface in the first die is determinedwhere a second die will bond to the first die. The second die and firstdie will mate according to how the bond pads in each respective die areconfigured to be coupled together. Once the interface is determined, thedummy metal bond pads around the periphery of the first or second diecan be removed from the design. In some embodiments, where the first andsecond die have the same sizes, the first die will interface with thesecond die across its entire surface. In some embodiments where thefirst or second die is smaller than the other, the interface between thetwo dies will be smaller than the entire surface area for one of thedies.

At step 1730, the dummy metal bond pads are removed from the layoutdesign in the first and second dies which are directly in line with aseal ring unit of either the first die or the second die. In otherwords, the dummy metal bond pads are removed from the layout design inthe first die where the second die's seal ring would be directly inline. Likewise, the dummy metal bond pads are removed from the layoutdesign in the second die which are directly in line with the seconddie's seal ring. This provides that the corresponding dummy metal bondpads in the each die are removed from the design.

FIG. 18 illustrates a flow diagram for altering a bond pad design toprovide a ring-like dummy bond pad which is coupled to a seal ring, inaccordance with some embodiments. In step 1810, a substantially uniformbond pad layout for a first die is created. A substantially uniform bondpad layout can include a layout of bond pads with no more than about 10%variation in pattern and/or bond pad sizes. At step 1820, an interfacein the first die is determined where a second die will bond to the firstdie. The second die and first die will mate according to how the bondpads in each respective die are configured to be coupled together. Insome embodiments, where the first and second dies have the same size,the first die will interface with the second die across its entiresurface. In some embodiments where the first or second die is smallerthan the other, the interface between the two dies will be smaller thanthe entire surface area for one of the dies.

At step 1830, after the interface is determined, the dummy metal bondpads are removed from the layout design in the first and second dieswhich are directly in line with a seal ring unit of either the first dieor the second die. In other words, the dummy metal bond pads are removedfrom the layout design in the first die where the second die's seal ringwould be directly in line. Likewise, the dummy metal bond pads areremoved from the layout design in the second die which are directly inline with the second die's seal ring. This provides that thecorresponding dummy metal bond pads in the each die are removed from thedesign.

At step 1840, the removed bond pads are replaced with a ring-like bondpads which are coupled to the underlying seal ring unit in step 1850.The coupling can be done by individual bond pad vias disposed along thering-like bond pads in some embodiments. In other embodiments, thecoupling can be done by a ring-like bond pad via disposed under thering-like bond pads which is physically and electrically coupled to boththe ring-like bond pads and the seal ring unit at the periphery of thedie. In some embodiments, the bond pad vias can be coupled to aninterconnect layer of the die.

Embodiments provide a way to increase bond yield by providing a betterhybrid bonding interface to provide fusion bonding of oxide materials intwo dies and direct metal-to-metal bonding of metal materials in the twodies. Removing dummy bond pads over the seal rings provides a betterbonding interface for fusion bonding oxide bonding layers. In someembodiments, after removing the dummy bond pads from the design, aring-like bond pad can be used which is coupled to the seal ring or aninterconnect of the die. Embodiments include wafer-on-wafer,chip-on-chip, and chip-on-wafer bonding where the die sizes may match ormay be different.

One embodiment is a structure including a first die. The first dieincludes a first oxide bonding layer having a first plurality of bondpads disposed therein and a first seal ring disposed in the first oxidebonding layer, where the first oxide bonding layer extends over thefirst seal ring. The structure further includes a second die. The seconddie includes a second oxide bonding layer having a second plurality ofbond pads disposed therein, where the first plurality of bond pads isbonded to the second plurality of bond pads, where the first oxidebonding layer is bonded to the second oxide bonding layer, and where anarea interposed between the first seal ring and the second oxide bondinglayer is free of bond pads.

Another embodiment is a method including determining an alignment of afirst die to a second die by aligning active bond pads of the first dieto corresponding active bond pads of the second die, where a first areaof the first die and a second area of the second die are aligned with aseal ring of the second die. All bond pads are removed in the first areaof the first die and in the second area of the second die. The first dieis bonded to the second die according to the alignment.

Another embodiment is a method including determining a first devicelayout of bond pads disposed at a surface of a first device. A seconddevice layout of bond pads disposed at a surface of a second device isdetermined, the second device having a seal ring. An alignment whichaligns a first active bond pad of the first device to a second activebond pad of the second device is determined, where the alignment causesthe seal ring to align with a first region of the first die. First bondpads in the first region are removed from the first device layout ofbond pads. Second bond pads are removed from a second region of thesecond device which align with the first bond pads according to thealignment. The first active bond pad is bonded to the second active bondpad. The first region is bonded to the second region.

One embodiment is a structure including a first die and a second diebonded to the first die. The first die includes a first bonding layer, afirst plurality of bond pads disposed in the first bonding layer, and afirst seal ring disposed at a periphery of the first die. The second dieincludes a second die bonded to the first die, the second die includes asecond bonding layer, a second plurality of bond pads disposed in thesecond bonding layer, a third plurality of bond pads comprising a subsetof the second plurality of bond pads, wherein the first plurality ofbond pads is respectively bonded to the third plurality of bond pads,and wherein an area interposed between the first seal ring and thesecond bonding layer is free of active bond pads.

Another embodiment is a method including aligning a first die to asecond die by aligning first bond pads of the first die to correspondingsecond bond pads of the second die, where a first area of the first dieis aligned with a second area of the second die. The second area of thesecond die corresponds to a location of a seal ring of the second die.The first area is free of active bond pads. The first die is bonded tothe second die, where a first edge of the first die is not aligned witha second edge of the second die.

Another embodiment is a device including a first device area and a firstinterconnect structure disposed over the first device area. The firstinterconnect structure is electrically coupled to the first device area.The first interconnect structure includes one or more insulating layers,one or more metallization layers disposed within the one or moreinsulating layers, and a seal ring structure embedded in the one or moreinsulating layers and disposed at a periphery of the first interconnectstructure. The device also includes a bond dielectric layer disposedover the first interconnect structure. The device further includes aseal ring metal embedded within the bond dielectric layer and physicallycoupled to the seal ring structure. The device also includes a first setof active bond pads disposed at a first surface of the bond dielectriclayer, each of the bond pads of the active bond pads electricallycoupled to the first interconnect structure by a corresponding metalvia. The device includes a first set of dummy bond pads disposed at thefirst surface of the bond dielectric layer. A keep out zone is in thebond dielectric layer, the keep out zone being free of any active bondpads, the keep out zone including a metal element.

Another embodiment is a structure including: a base die including afirst plurality of bond pads disposed at an upper surface of the basedie at a die attach area, a second plurality of bond pads disposed atthe upper surface of the base die outside the die attach area, and akeep out area interposed between the first plurality of bond pads andthe second plurality of bond pads, the keep out area free of bond pads.

Another embodiment is a method including aligning first bond pads of afirst die to second bond pads of a second die and aligning a first bondpad free region of the first die with a second bond pad free region ofthe second die. The method also includes and fusing a dielectricmaterial in the first bond pad free region with a dielectric material inthe second bond pad free region.

Another embodiment is a device including a first device area. The devicealso includes a first interconnect structure disposed over the firstdevice area. The device also includes a first dielectric layer disposedover the first interconnect structure. The device also includes a sealring structure embedded in the first dielectric layer, the seal ringstructure disposed at a periphery of the first dielectric layer. Thedevice also includes bond pads disposed at an upper surface of the firstdielectric layer, the bond pads distributed across the upper surface ofthe first dielectric layer in a regular pattern except in a keep outzone of the first dielectric layer, the bond pads including a set ofactive bond pads and a set of dummy bond pads, each of the bond pads ofthe set of active bond pads electrically coupled to the firstinterconnect structure by a corresponding metal via, the keep out zonefree of the bond pads.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A structure comprising: a base die, the base diecomprising: a first plurality of bond pads disposed at an upper surfaceof the base die at a die attach area, a second plurality of bond padsdisposed at the upper surface of the base die outside the die attacharea, and a keep out area interposed between the first plurality of bondpads and the second plurality of bond pads, the keep out area free ofbond pads.
 2. The structure of claim 1, wherein the base die furthercomprises a first bonding layer laterally surrounding the firstplurality of bond pads and the second plurality of bond pads, whereinthe first bonding layer is fused to a second bonding layer of an upperdie.
 3. The structure of claim 1, further comprising a ring-like bondinglayer disposed at an upper surface of the base die in the keep out area.4. The structure of claim 1, further comprising: an upper die (312)bonded to the base die, the upper die comprising: a third plurality ofbond pads (342) disposed at a lower surface of the upper die, the thirdplurality of bond pads bonded to the first plurality of bond pads, and asecond seal ring embedded in the upper die, the second seal ring alignedto the keep out area of the base die.
 5. The structure of claim 4,wherein the first plurality of bond pads is directly bonded to the thirdplurality of bond pads in a metal-to-metal bond which is free of aeutectic material.
 6. The structure of claim 4, wherein the base diefurther comprises a first seal ring, wherein the first seal ring and thesecond seal ring are aligned on a first edge of the upper die.
 7. Thestructure of claim 6, wherein the second seal ring is laterallyseparated from the first seal ring along a second edge of the upper dieand corresponding second edge of the base die.
 8. A method, comprising:aligning first bond pads of a first die to second bond pads of a seconddie and aligning a first bond pad free region of the first die with asecond bond pad free region of the second die; and fusing a dielectricmaterial in the first bond pad free region with a dielectric material inthe second bond pad free region.
 9. The method of claim 8, wherein thefirst bond pads are distributed across a face of the first die in aregular pattern except in the first bond pad free region, wherein thesecond bond pads are distributed across a face of the second die in aregular pattern except in the second bond pad free region.
 10. Themethod of claim 8, wherein the second bond pad free region correspondsto a location of a seal ring of the second die.
 11. The method of claim10, wherein the first bond pad free region corresponds to an interiorregion of the first die.
 12. The method of claim 8, further comprising:directly bonding a metal of the first bond pads to a metal of the secondbond pads without using a solder material.
 13. The method of claim 8,further comprising: bonding a first surface bonding ring of the firstdie to a second surface bonding ring of the second die to electricallycouple a seal ring structure of the second die to a metal feature of thefirst die.
 14. The method of claim 13, wherein the metal feature of thefirst die is a seal ring structure of the first die.
 15. The method ofclaim 8, wherein an edge of the second die after the fusing is alignedto an interior portion of the first die.
 16. A device comprising: afirst device area; a first interconnect structure disposed over thefirst device area; a first dielectric layer disposed over the firstinterconnect structure; a seal ring structure embedded in the firstdielectric layer, the seal ring structure disposed at a periphery of thefirst dielectric layer; and bond pads disposed at an upper surface ofthe first dielectric layer, the bond pads distributed across the uppersurface of the first dielectric layer in a regular pattern except in akeep out zone of the first dielectric layer, the bond pads including aset of active bond pads and a set of dummy bond pads, each of the bondpads of the set of active bond pads electrically coupled to the firstinterconnect structure by a corresponding metal via, the keep out zonefree of the bond pads.
 17. The device of claim 16, further comprising aring-like metal bonding structure disposed at a surface of the keep outzone.
 18. The device of claim 17, wherein the ring-like metal bondingstructure is electrically coupled to the seal ring structure.
 19. Thedevice of claim 17, wherein the ring-like metal bonding structure iselectrically coupled to a seal ring structure of a second device. 20.The device of claim 16, wherein the keep out zone is interposed betweena first active bond pad of the set of active bond pads and a seconddummy bond pad of the set of dummy bond pads, the second dummy bond padbeing disposed over the seal ring structure.